Prompt treatment with tissue plasminogen activator (tPA, also known as alteplase) "is a very effective means of limiting the degree of disability in stroke patients," study co-author Dr. Jonathan Emberson, of University of Oxford in the U.K., said in a news release from the journal The Lancet.

The study, published in the journal on Aug. 5, also reinforces the idea that the quicker that patients can get tPA, the better.

One U.S. expert agreed. "The analysis reiterates the importance of patients going to the ER immediately at the time of developing acute neurological symptoms that could be due to a stroke," said Dr. Rafael Alexander Ortiz, director of interventional neuroradiology and stroke at Lenox Hill Hospital in New York City.

Clot-busting drugs are used to treat people who have suffered an ischemic stroke, which occurs when a clot blocks blood flow to the brain.

In the study, Emberson's team looked at data from more than 6,700 stroke patients who took part in nine clinical trials involving tPA.

The likelihood of a good outcome -- defined as no significant disability three to six months after stroke -- were 75 percent higher for patients who received the drug within three hours of initial stroke symptoms, compared with patients didn't get tPA.

While that three-hour window is ideal, even patients who got tPA a bit later received some benefit. For example, the chances of a good outcome were still 26 percent higher among patients who received the clot-buster within 4.5 hours of the attack, and 15 percent higher for those who received the drug more than four to five hours after initial stroke symptoms, the group found

The benefits of quick treatment with tPA were seen in all patient groups, including those older than 80 and those with severe strokes, the authors add.

There was a slight added risk with the drug, however: the researchers also found that tPA increased the risk of dying from brain bleeding by about 2 percent within the first few days after stroke.

One U.S. stroke expert called the new review "powerful."

"The information is very significant because it helps support our concept of 'time is brain' by showing that faster treatment times do result in better outcomes for patients," said Dr. Keith Siller, director of the Stroke Consultative Services at North Shore-LIJ's Cushing Neuroscience Institute in Manhasset, N.Y.

He said that the finding that tPA helped even elderly patients was key, because "there has been a negative bias about offering IV tPA because of concerns about decreased clinical benefit and increased hemorrhage in this subset of patients."

In the Lancet news release, study co-author Kennedy Lees, a professor of cerebrovascular medicine at the University of Glasgow, in Scotland, said that "what this shows is that we are up against the clock when treating ischemic stroke. Every minute counts. People need to be identified quickly and systems need to be in place to get them scanned, diagnosed accurately and then treated within minutes to hours."

More information

The American Heart Association/American Stroke Association has more about stroke treatments.